This invention relates generally to processes for the commercial manufacture of fat-containing dry milk or flavored dry milk in the form of aggregates which can be readily dispersed in water to form a stable reconstituted milk. Also, it pertains to products resulting from such processes.
So-called instant dry milk is widely manufactured and sold in the United States and other countries. As disclosed in Peebles U.S. Pat. No. 2,835,586 dated May 20, 1958, the process involves supplying nonfat anhydrous dry milk powder to an agglomerating chamber where the particles are moistened and commingled to cause formation of random porous aggregates. These aggregates, which in typical instances may have a total moisture content of the order of from 10 to 15%, are then subjected to secondary drying to remove excess moisture. Such instant nonfat dry milk can be readily reconstituted in cold water by simple stirring and without vigorous agitation. The process of said Pat. No. 2,835,586 can be used to agglomerate anhydrous spray dried fat-containing dry milk as well as spray dried nonfat milk powder. However, instant fat-containing milk made in this fashion has impaired wettability and dispersibility in water, and the reconstituted milk is subject to fat separation or creaming off.
Subsequent to the development of the above Peebles process, it was found that an acceptable fat-containing agglomerated dry milk could be formed by the use of lecithin. As described in U.S. Pat. No. 3,164,473 dated Jan. 5, 1965, lecithin is supplied in such a fashion that in the final agglomerated product it is in the form of extraneous lecithin distributed on the powder particles and agglomerates. The use of lecithin as described in said U.S. Pat. No. 3,164,473 makes it possible to produce a fat-containing instant dry milk which can be reconstituted in cold water. However, it makes use of fat-containing spray dried milk powder as a source material. An improved process making use of the process of U.S. Pat. No. 3,164,473 is disclosed in U.S. Pat. No. 3,300,315 dated Jan. 24, 1967. The improved process likewise makes use of fat-containing milk as a source material. The liquid fat-containing milk is spray dried to form a moist powder which is passed through an agglomerating chamber into which an atomized mixture of steam, water and lecithin is introduced. The resulting aggregates, after removal of excess moisture, having relatively good dispersibility in cold water. The processes of U.S. Pat. Nos. 3,164,473 and 3,300,315 have been used for the commercial manufacture of acceptable instant dry milk products having a fat content of the order of 5%. However, since plants using such processes are dependent upon use and availability of fat-containing spray dried milk, they require placement in a fluid milk shed, high capital investment in central locations (e.g., for evaporators, spray dryers, instantizers, etc.) and involve high transportation costs when the product is distributed nation-wide. In contrast with the nonfat dry milk powder, which is widely available commodity, spray dried fat containing milk is not widely available and requires storage under special conditions to prevent deterioration by oxidation.
U.S. Pat. No. 2, 911,300 dated Nov. 3, 1959, proposes to produce a dry instant milk product containing fat by first forming nonfat milk solids in the form of aggregates, and after drying to remove excess moisture, fat in molten form is applied to the surfaces of the aggregates. As pointed out in said Pat. No. 2,911,300, such a product can be dispersed in warm water. The patent further proposes the use of a fat-water emulsion of the type disclosed in Peebles et al. U.S. Pat. No. 2,622,984 dated Dec. 23, 1952, which consists of fat and water together with a soluble caseinate. This mixture is subjected to homogenizing as ordinarily applied in tthe milk industry, after which it is atomized and applied to the previously formed dry aggregates and the aggregates again dried to remove excess moisture. U.S. Pat. No. 2,911,300 also refers to the use of lecithin as an emulsifier in preparing the emulsion of U.S. Pat. No. 2,622,984, in place of part or all of the caseinate content. While the process of U.S. Pat. No. 2,911,300 makes use of nonfat milk solids as a source material, it first forms and then dries the nonfat milk aggregates, and thereafter in a separate step the atomized fat emulsion is applied. Since some moisture is added with the fat, the moisture content of the aggregates is increased, thus requiring another stage of secondary drying. The several steps add to processing costs and thus the process is relatively uneconomical. Also this process is subject to other difficulties, particularly in that some fat separation tends to occur in the reconstituted milk, and the amount of separating fat increases for the higher fat contents. Since the lecithin (when used) is incorporated in the fat emulsion as an emulsifying agent, it does not function as extraneous lecithin to produce good wettability.